Beth Gibbons from Portishead performs on the Other stage at Glastonbury 2013. Photograph: Anthony Devlin/PA

Glastonbury festivalgoers always seem pretty bloody pleased with themselves so who better then to pour a bracing bucket of water over everything than Portishead, a band whose musical output has slowly – three albums in 19 years, the last half a decade ago – grown increasingly icy, never mind the grumpy old man persona that Geoff Barrow has cultivated on Twitter?

Pitted against Arctic Monkeys on the Pyramid stage and arguably an equally big draw in Chic at West Holts, the trip-hop group (younger readers can look up the term) were magnificently compelling, a reminder that sometimes it pays to work just that little bit harder for life's pleasures.

Given the slim nature of the band's catalogue, it might be easy to think that the group would ply a heritage approach, but there was nothing backward-looking in the way Portishead sound. Perhaps that's testament to the paucity of acts of their ilk since their initial mid-90s heyday.

The opening is a statement of intent, a seven-minute extended version of Silence (the opening track on the prosaically titled Third), the sound driving forward with hypnotic force, with Beth Gibbons (left) singing: "Tempted in our minds/ Tormented inside lie …"

The meeting of Barrow's hip-hop sensibility, Adrian Utley's feeling for filmic textures and that extraordinary voice, like something bloodily ripped from Nature, remains utterly transfixing, exemplified on songs such as The Rip.

It feels like a testament to the audience's taste in general that they surrendered to them: as well as that old warm affection, there's an appetite for this. This was not least the case when David Cameron made a surprise appearance - his image superimposed on the video screens, with red lasers shooting out his eyes - a reminder that as someone else once said, anger is an energy.

The closing We Carry On proved a motorik beast, the sound of the inside of the mind of Winston Smith. It went on so long that if left time for Beth Gibbons to clamber down to hug those at the front of the crowd. Then when it ended, the famously least-starry frontwoman in music said goodbye with the words: "Thank you so much ... I hope it was all right."